Development of LiFeO₂-LiCoO₂-NiO cathodes for molten carbonate fuel cells

The phase relationships in the LiFeO₂-LiCoO₂-NiO ternary system were determined and used to find compositions that would reduce the resistivity of LiFeO₂-containing cathodes to levels low enough for molten carbonate fuel cells. There was no solubility limit in the NiO-LiFeO₂ binary system; a continuous solution was formed. Two regions of homogeneity were found in the LiFeO₂-LiCoO₂ binary, 0 to 13 and 87 to 100 mol % LiCoO₂. Similarly, two regions of homogeneity were found in the LiCoO₂-NiO binary, 0 to 18 and 94 to 100 mol % LiCoO₂. The resistivities of these materials indicate that addition of Ni and Co to the LiFeO₂ lattice decreases the resistivity from about 300 Ω cm to about 1 to 10 Ω cm at 650°C. Using both Ni and Co additives together reduces the resistivity of LiFeO₂ and its sensitivity to CO₂ partial pressure. Cell tests indicate that solid solutions LiFeO₂-LiCoO₂-NiO system possess electrocatalytic activity. The cell displayed a potential of 0.79 V at 160 mA/cm². The data indicate that LiFeO₂-LiCoO₂-NiO cathodes hold promise for fuel-cell cathodes.